Surgical lasers such as lasers used for transmyocardial revascularization (TMR) must provide accurate repeatable performance in order to insure proper safe operation on a beating human heart. Typically a CO.sub.2 laser is used to generate a laser beam which is propagated through an articulated arm and a lens cell to a handpiece manipulated by the surgeon to direct the beam at the proper time, place and power to strike a hole in the heart wall precisely and safely. The handpiece generally has a contact surface at its distal end for contacting the beating heart and an aperture in that surface to allow the laser beam to exit and strike the heart wall. The lens cell contains a lens which focuses the laser beam near, at or beyond the contact surface so as to concentrate the beam energy at the desired site on the heart wall. A window in the handpiece above the contact surface provides a path for the ablative issue of the heart to pass out without contaminating the remainder of the handpiece, the lens cell and other components and optics upstream of it. Nevertheless, some steam, smoke and debris inevitably do find their way to the handpiece and lens cell and contaminate them and impair their optical efficiency.
To overcome this the parts are cleaned and sterilized after each use. However, it has been observed that the cleaning or sterilization itself can damage and degrade the lens in the lens cell. Typically these lenses are made of zinc selenide (ZnSe) which is highly corroded by the sterilizing, cleaning medium ethylene oxide (EtO). The EtO is generally applied over a three-hour period at 100% humidity and 130.degree. C. temperature which seriously deteriorates among other things the anti-reflective coating on the lens. Without the coating as much as 15% of the light can be reflected back to the laser causing heating and damage. More importantly, the beam incident at the patient's heart will contain 15% less energy than the surgeon has called for and expects.
Also during the cleaning process encrusted blood, body fluids or tissue may require a nurse or attendant to physically remove the debris such as by rubbing or scraping, which can seriously damage the lens so that its focus is shifted or it is without focus, or the transmission properties can be otherwise interfered with or impaired.